1. Field of the Invention
The present invention relates to a glass ceramic sintered product having a highly thermally expanding property. More particularly, the invention relates to a glass ceramic sintered product useful as an insulating substrate for preparing a wiring board used in a package for containing a semiconductor.
2. Description of the Prior Art
A wiring board used for various kinds of electronic circuit parts has a structure in which a metallized wiring layer is formed on the surface or inside of the insulating substrate. A representative example of the electronic circuit part equipped with the wiring board may be a semiconductor device-containing package containing a semiconductor device such as LSI (large-scale integrated circuit device).
In such a semiconductor device-containing package, in general, a semiconductor device is mounted on the surface of a ceramic insulating board such as of alumina ceramic, a metallized wiring layer such as of W or Mo is formed on the surface or inside of the insulating substrate, a plurality of connection pads are formed on the back surface of the insulating substrate being connected to the metallized wiring layer, and connection terminals are attached to the connection pads for making connection to the external circuit board. Further, the semiconductor device mounted on the surface of the insulating substrate is connected to the metallized wiring layer through wires and is air-tightly sealed with a closure.
The above-mentioned semiconductor device-containing package is mounted on an external circuit board by electrically connecting the connection terminals attached to the connection pads on the back surface of the insulating substrate to the wiring conductors of the external circuit board by soldering or the like method.
Here, however, an increase in the degree of integration of the semiconductor device is accompanied by an increase in the number of electrodes formed on the semiconductor device and by an increase in the number of connection terminals of the package that contains the semiconductor device. In practice, however, it has been desired to realize the semiconductor device-containing package in a small size, and limitation is imposed on increasing the size of the package despite of an increase in the number of electrodes of the semiconductor device. It has therefore been urged to form a number of connection terminals on a more compact semiconductor device-containing package, i.e., to enhance the density of the connection terminals.
As packages having highly densely arranged connection terminals, there have heretofore been known a pin grid array (PGA) having metal pins such as of Kovar connected to the back surface (lower surface) of a insulating substrate, a quad flat package (QFP) having a structure in which metal pins of the shape of a gull-wing (L-shape) are drawn from all of the four side walls of the package, and a ball grid array (BGA) comprising ball terminals which are connection terminals formed of a brazing material such as solder. Among them, it has been said that the BGA is most suited for highly densely arranging the connection terminals.
In the above-mentioned ball grid array (BGA), the ball terminals of a brazing material are brought into contact with the wiring conductor of the external circuit board, and are heated and melted at a temperature of from about 250 to about 400xc2x0 C. and are joined to the wiring conductor so as to effect the mounting on the external circuit board. Owing to such a mounting structure, the electrodes of the semiconductor device mounted on the semiconductor device-containing package are electrically connected to the external circuit board through the metallized wiring layer and the connection terminals.
Ceramics such as alumina and mullite have heretofore been used as a ceramic insulating substrate have a strength of as high as 200 MPa or more, and are useful from the standpoint of forming a laminated layer structure together with the metallized wiring layer maintaining high reliability. These ceramics, however, have a defect in that their coefficients of thermal expansion are as low as from about 4 to about 7 ppm/xc2x0C. That is, a printed board having a Cu wiring layer formed on a glass-epoxy insulating layer has been most widely used as an external circuit board on which a package will be mounted. This printed board has a coefficient of thermal expansion of as very large as from 11 to 18 ppm/xc2x0C. Therefore, when the semiconductor device-containing package is mounted on the external circuit board such as the printed board, heat generated by the operation of the semiconductor device is applied to both the insulating substrate and the external circuit board, resulting in the occurrence of thermal stress due to a difference in the thermal expansion between the insulating substrate and the external circuit board. As a result, the thermal stress affects the connection portion between the insulating substrate and the external circuit board, giving rise to the occurrence of cracks and peeling of the connection terminals, making it difficult to stably maintain the package electrically connected to the external circuit board for extended periods of time.
The present inventors therefore have previously proposed a glass ceramic sintered product obtained by mixing, with a predetermined filler, a glass containing BaO in an amount of from 15 to 60% by weight and having a low softening point and a highly thermally expanding property, and firing the mixture. The insulating substrate formed of this glass ceramic sintered product has a large coefficient of thermal expansion. Therefore, the wiring board equipped with this insulating board effectively prevents the occurrence of cracks or peeling of the connection terminals caused by the thermal stress, and makes it possible to stably maintain the electric connection between, for example, the semiconductor device-containing package and the external circuit board for extended periods of time.
However, the above BaO-containing glass ceramic sintered product has poor resistance against the chemicals, and is discolored when it is treated with an acidic solution or an alkaline solution used in the step of plating. Further, when a metallized wiring layer of a low-resistance metal such as copper is formed by co-firing on the surface of the insulating substrate formed of the glass ceramic sintered product, there arouses a problem in that the metallized wiring layer loses the strength of adhesion.
The object of the present invention, therefore, is to provide a high-thermal-expansion glass ceramic sintered product formed by using a BaO-containing glass and having excellent resistance against the chemicals, and a method of producing the same.
Another object of the present invention is to provide a wiring board comprising an insulating substrate of the glass ceramic sintered product and a metallized wiring layer formed on the surface or inside of the insulating substrate, featuring improved adhesion between the metallized wiring layer and the insulating substrate.
A further object of the present invention is to provide a structure for mounting the wiring board (particularly, a semiconductor device-containing package) maintaining a strong and stable connection to the external circuit board that contains an organic resin for extended periods of time.
According to the present invention, there is provided a high-thermal-expansion glass ceramic sintered product comprising:
(A) a glass phase which contains BaO in an amount of from 5 to 60% by weight; and
(B) a filler phase containing metal oxide particles having a coefficient of linear thermal expansion at 40 to 400xc2x0 C. of not smaller than 6 ppm/xc2x0C.;
wherein said sintered product contains:
(C) a Zr element in an amount of from 0.1 to 30% by weight calculated as ZrO2, and
has a coefficient of linear thermal expansion at 40 to 400xc2x0 C. of from 8.5 to 18 ppm/xc2x0C.
According to the present invention, there is further provided a method of producing a glass ceramic sintered product comprising preparing a mixture which contains a glass powder containing BaO in an amount of from 5 to 60% by weight, a metal oxide powder having a coefficient of linear expansion at 40 to 400xc2x0 C. of not smaller than 6 ppm/xc2x0C., and a Zr element in an amount of from 0.1 to 30% by weight calculated as ZrO2, and molding said mixture into a predetermined shape followed by firing at 800 to 1100xc2x0 C.
According to the present invention, there is further provided a wiring board comprising an insulating substrate formed of the glass ceramic sintered product and a metallized wiring layer formed on the surface or inside of said insulating substrate.
The invention further provides a structure for mounting the wiring board, wherein the wiring board is placed on an external circuit board having a wiring conductor formed on an insulating layer containing an organic resin, and the connection terminals of said wiring board are joined by brazing to said wiring conductor, said wiring board having a semiconductor device air-tightly sealed in the surface of said insulating substrate, and having connection terminals on the back surface of said insulating substrate so as to be electrically connected to said semiconductor device.
If briefly described, the glass ceramic sintered product of the present invention is obtained by firing a BaO-containing glass powder and a filler powder containing metal oxide particles having a coefficient of linear thermal expansion at 40 to 400xc2x0 C. of not smaller than 6 ppm/xc2x0C., and has a highly thermally expanding property. What is particularly important here is that the glass ceramic sintered product contains a Zr element in an amount of from 0.1 to 30% by weight calculated as ZrO2. That is, upon containing the Zr element in a predetermined amount, the glass ceramic sintered product of the invention exhibits excellent resistance against the chemicals and is not discolored even when it is treated with an acidic solution or an alkaline solution in, for example, a step of plating. A sintered product containing the above Zr element, the BaO-containing glass and metal oxide particles having a large coefficient of linear thermal expansion, exhibits a coefficient of linear thermal expansion at 40 to 400xc2x0 C. of from 8.5 to 18 ppm/xc2x0C. Therefore, the wiring board using the glass ceramic sintered product as an insulating substrate exhibits a coefficient of linear thermal expansion which is close to the coefficient of linear thermal expansion (e.g., 11 to 18 ppm/xc2x0C.) of the external circuit board such as the printed board. There is thus obtained a mounting structure which effectively suppresses the occurrence of thermal stress caused by a difference in the thermal expansion between the two, and effectively prevents the occurrence of cracks or peeling of the connection terminals at the connection portion between the two. Further, the insulating substrate has the coefficient of linear thermal expansion close to the coefficient of linear thermal expansion of the metallized wiring layer of a low-resistance conductor formed on the surface or inside thereof (copper has a coefficient of linear thermal expansion of 18 pm/xc2x0C.). This enhances the adhesion between the metallized wiring layer and the insulating board.
Upon containing the Zr element, further, an unexpected advantage is accomplished such as suppressing the precipitation of cristobalite. That is, the starting glass powder of the glass ceramic sintered product usually contains an SiO2 component which causes cristobalite to be partly precipitated at the time of sintering. The sintered product precipitating the cristobalite has a point of inflection on a curve of the coefficient of linear thermal expansion at 40 to 400xc2x0 C. Therefore, the wiring board having the insulating substrate formed by using the above sintered product involves a problem in that microcracks develop in the insulating substrate due to heat impairing the properties of the wiring board. For example, when the semiconductor device-containing package having the semiconductor device placed on the wiring board, is mounted on an external circuit board such as printed board, a difference in the size increases between the region where the cristobalite crystals have precipitated in the insulating substrate and the region where they were not precipitated due to heat generated by the operation of the semiconductor device, giving rise to the occurrence of microcracks in the insulating substrate. On the other hand, the glass ceramic sintered product of the present invention in which the Zr element is made present, suppresses the precipitation of cristobalite. Therefore, the wiring board equipped with the insulating substrate formed of the sintered product effectively prevents the occurrence of microcracks in the insulating substrate.